Most samples of chemical interest are complex mixtures, making the usual combination of chromatography with mass spectrometry (MS) a natural choice. However, the increased demand for chemical analysis by mass spectrometry in many areas of science makes it imperative to increase efficiency of analysis by minimizing sample workup and overall analysis time, which makes direct mixture analysis highly desirable. These demands were in many ways solved in 2004 with the development of ambient mass spectrometry, a branch of mass spectrometry which allows spectra to be recorded on samples in their native state with minimal or no sample preparation. Ambient ionization provides the speed needed for in situ experiments by recording mass spectra instantaneously on unmodified samples in their native state and in the ambient environment. Sample analytes are loaded onto a substrate material for sampling and supporting the analytes to be studied. Nonpolar substrate surfaces currently used in ambient MS offer an advantage over other existing materials in the analysis of a variety of analytes but have limited utility in that they often are impure, mechanically weak, single use, offer poor sample loading, have decreased signal intensity and stability, and are not easy to modify, making them useful for only a particular class of analytes. As an alternative to the more widely used sampling materials, such as paper and glass, we have developed novel organosiloxane (OSX) polymer materials that have the potential to be used as sampling substrates in ambient ionization methods. Our materials can be chemically tuned to increase signal intensity, molecule selectivity, signal stability, and can also be chemically modified by covalent attachment of molecules to serve different analytical purposes, within many other possibilities. In Aim 1, we will investigate and optimize the synthetic parameters that affect the polymer features such as its porosity, polarity (hydrophobicity/hydrophilicity), and its surface features and chemistry. In Aim 2, we will use the OSX polymer as a sampling material in spray ionization and desorption electrospray ionization (DESI-MS) to evaluate the performance of the polymer and to identify the optimal operating conditions, signal intensity and stability for the polymers investigated and designed in Aim 1. In Aim 3, we will evaluate the feasibility of coupling the polymers to as commercial ambient MS, using Prosolia's commercial robotic sources. To assess the utility of these OSX polymers as sampling materials, we will analyze drugs in blood / serum and study in situ digestion of proteins on polymer surfaces grafted with an enzyme. Given the many advantages of OSX polymers, they will make excellent commercial products that can widen the application of ambient ionization MS in many different areas, including clinical/medical diagnostics and proteomics.